A generally known sensor for detecting a rotation angle uses a potentiometer.
A sensor using the potentiometer is a contact type sensor, and therefore, the device suffers from a shortened life because of friction.
With the development of remarkable magnets in these years, non-contact type sensors utilizing a magnetic detecting element are being used in various ways. Since the sensor utilizing a magnet and a magnetic detecting element is a non-contact type, its life can be made long, and a potentiometer which is expensive is not needed. Therefore, the sensor can be produced inexpensively.
To detect a rotation angle by a non-contact type sensor using a magnetic detecting element, it is desired that the angle is magnetically detected by the magnetic detecting element. At this time, an air gap is secured between the magnet and the magnetic detecting element without fail, magnetic flux of a magnetic circuit is guided in a predetermined direction to configure a stable magnetic circuit. Besides, this type of sensor is demanded to prevent accuracy from being degraded due to performance of parts or an error in production, thus improving reliability.
In view of above, the present invention aims to provide a sensor which secures an air gap between the magnet and the magnetic detecting element without fail, guides magnetic flux of a magnetic circuit in a predetermined direction to configure a stable magnetic circuit, and improves reliability.
Lately, attention is being attracted by an electric bicycle provided with an electric motor for assisting human power. This type of electric bicycle is structured by mounting an electric motor and a battery power source for supplying power to the motor on an ordinary bicycle to add a predetermined motor auxiliary power depending on a human power driving force, thereby reducing a load on a human power drive force. And, the auxiliary drive force by a motor is legally limited not to exceed the human power drive force in Japan, and when a running speed does not exceed 15 Km/h, assistance by the motor is 100%, and when the running speed exceeds 15 Km/h, assistance is decreased gradually, then when the speed is 24 Km/h or more, control is made to stop the assistance by the motor. Thus, a human power assisting ratio is restricted to be variable in accordance with the running speed.
As shown in FIG. 54, such an electric bicycle 1 is basically formed of an ordinary bicycle which is provided with a front wheel 4 and a rear wheel 5 at the front and rear of its frame, and driven by leg power via the rear wheel 5. According to the Japanese Industrial Standards (JIS), the member indicated by reference numeral 2 is called a main pipe and the member indicated by reference numeral 2d is called a seat pipe, and the same designation by the JIS standards is used in this specification.
This auxiliary drive means J comprises a motor M which is disposed at right angles with the axle and in the neighborhood of the middle in the breadth direction of the vehicle body, a power transmission (not shown) which changes the rotating drive force of the motor towards a direction that the axles are rotated and also decrease the speed, and a combining mechanism (not shown) which combines the decelerated rotating drive force of the motor with an ordinary drive system of the human power drive force and separates the motor drive system from the ordinary drive system when the bicycle is driven by the human power drive force only.
The motor drive system is driven to rotate by the power transmission device with the motor M as the drive source, and the Motor M is supplied with electric power by an electric power device. Specifically, this electric power device comprises a battery power source using a plurality of storage batteries, an electric power circuit which stabilizes and supplies electric power, a motor for running, a motor drive circuit which directly controls the rotations of the motor, and a control circuit which outputs a speed command value and the like to the motor drive circuit. And, the rotation drive force of the motor is added to a conventional drive system and transmitted to the running wheel through the transmission device, thereby running the bicycle.
And, as a method for detecting the human power drive force, it is known to detect the magnitude of a human power drive force in view of a reaction force which is applied to the gears of a planetary gear (e.g., Japanese Patent Laid-Open Publication No. Hei 4-358987).
But, the electric bicycle described above detects the human power drive force at a position where the human power drive force is applied. And, it is disadvantageous that the device itself becomes large and heavy because its structure needs to withstand the human power drive force.
And, when the conventional electric bicycle uses a potentiometer as the sensor, a contact's life is shortened due to a frictional resistance, looseness or the like of respective gears. As a result, there is a disadvantage that satisfactory accuracy of measuring human power torque can not be secured.
In view of above, the present invention proposes a drive force auxiliary device which can improve detection performance and durability, applies the above-described sensor to this auxiliary device, thus its zero point can be compensated without fail; respective gears can be prevented from getting loose, and satisfactory accuracy of measuring human power torque can be secured.
The motor for the drive force auxiliary device is an ordinary brush DC motor, which is formed, for example, by accommodating in a motor case having a predetermined shape a rotor core having a plurality of exciting coils and formed in a cylindrical shape and a stator core disposed on the outer periphery of the rotor core; the rotor itself is fixed to a motor shaft which is rotatably supported in the case, and the brush is fixed to the motor case side to supply a drive electric current to the exciting coils of the rotor through the motor shaft. Therefore, with the rotations of the rotor, the contact point of the motor shaft is variable with respect to the brush, and the drive electric current is supplied to the exciting coils of the rotor according to the rotation condition. Specifically, by the brush which is a mechanical contact switch mechanism, electric current continuously supplied to the respective exciting coils is switched with the rotations of the rotor, and the direction of electric current is changed, thereby producing a rotation magnetic field to continue the electromagnetic rotation drive of the rotor.
Besides, this motor drive system has the motor output controlled based on the human power entered into the human power drive means by the rider and the running speed of the vehicle.
Specifically, there are disposed a torque sensor (the leg power detection means for the bicycle) for detecting the drive force by the human power of the rider and a vehicle speed detecting means for detecting the running speed of the bicycle, and their output terminals are connected to the control circuit through wiring.
Known detection methods used for the torque sensor include a method that an exclusive detection member is disposed on the transmission route of the human power to detect a torsion angle of the detection member according to the human power torque and expansion in the longitudinal direction, and a method that an elastic member is mounted between an input side rotor to which leg power is transmitted and an output side rotor, and the magnitude of a human power drive force between the input side rotor and the output side rotor is detected in view of a reaction force applied to the gears of a planetary gear (e.g., Japanese Patent Laid-Open Publication No. Hei 4-358987).
And, the vehicle speed detection means is formed of an exclusive rotating speed sensor which is connected to the pedal shaft via a gear mechanism because an ordinary brush DC motor is used as the auxiliary drive motor. Therefore, a running speed of the bicycle is obtained from the rotating speed of the pedal shaft.
And, by this control circuit, the above-described ratio of human power assistance is determined based on the running speed detected by the vehicle speed detection means at that time. This ratio is multiplied with the human power detected by the torque sensor to calculate an actually needed assisting output, and a motor output command value which satisfies the assisting output is outputted to the motor drive circuit. And, setting of this output value is effected by stepwisely calculating from both detection values by a calculation formula provided in the control means or by directly cross-referring both values from a predetermined table.
As described above, the motor is an ordinary brush DC motor, which is structured by accommodating a rectifier for commutation, a brush, a brush holder and the like in the axial direction, resulting in a disadvantage that the motor is long in the axial direction. Besides, there are disadvantages that the life of the motor is short because the brush is abraded and the bearing member such as a bearing is damaged by abraded dust produced.
On the other hand, when the torque sensor for detecting the human power drive force is exposed outside the vehicle body, it may be damaged or suffer from a heavy impact even if it is not damaged when the bicycle falls, thus the sensor may fail, and reliability is lowered. And, since it is directly exposed to effects from external natural atmosphere such as rain and wind or those such as dust and mud arising while the vehicle is running, reliability in view of error detection may be lost or the life of the device may be shortened. Besides, although such disadvantages can be solved by accommodating the torque sensor within a casing, the torque sensor is required to be made small in order to be disposed in the neighborhood of the crank shaft in the casing. But, it is hard to make the torque sensor small while keeping the needed detection accuracy.
Besides, since the exclusive vehicle speed sensor is disposed to obtain a vehicle speed to control the auxiliary drive, there is a disadvantage that the cost cannot be reduced sufficiently.
Specifically, the exclusive speed sensor and a space for it are needed, and wiring for it limits and complicates the design by the layout of wiring, assembling needs lots of labor, making it difficult to reduce the cost. Particularly, the running speed is needed to decide the human power assisting ratio of the electric bicycle and inevitable for the drive force assisting control. Therefore, the sensor is required to have satisfactory reliability in detecting the speed. And, to obtain a highly reliable speed sensor, expensive parts are used, and the speed sensor is required to be accommodated into a casing which is shielded from the external environments. Thus, cost reduction is inhibited.
Therefore, the present invention uses a brushless DC motor to configure a drive force assisting means, and accommodates its power assisting unit into a single casing as a unit to save space. And, a rotor rotation position detection means previously disposed on the brushless DC motor is also used as a running speed sensor. Thus, the invention aims to provide a drive force auxiliary device which can be very reliable and inexpensive.
The conventional electric bicycle described above uses the torque sensor to detect the human power drive force. This type of torque sensor always needs to match the torque sensor detection value when human power has not been entered by the user with a predetermined value indicating that the human power torque is zero. Therefore, a mechanism for mechanically making zero adjustment or an electrically adjusting element is generally disposed on the torque sensor.
Specifically, if this mechanism or adjusting element is not disposed, the detection value of the torque sensor includes an error, and the electric bicycle cannot be controlled properly. And, a comfortable human power assisting feeling cannot be obtained, and even when human power is not entered, the torque sensor detects an erroneous torque value, the electric bicycle may run by itself, concept of human power assistance is not satisfied, and it is not desirable in view of safety. Especially, in the electric bicycle which effects motor assistance according to the detected human power, it is essential that the motor auxiliary output is not effected when human power is not entered, namely the bicycle does not run by itself. And, the operation state of the torque sensor when human power is not entered is required as a standard point of zero for calibration of measuring accuracy.
This torque sensor is generally structured that human power torque entered through the pedals is converted by a mechanical structure into a physically displaced quantity such as a rotation angle according to the human power torque, and the displaced quantity (rotation angle) is measured by a displaced quantity sensor (rotation angle sensor). Specifically, the displaced quantity sensor converts into an electrical signal having a voltage or current volume proportional to the displaced quantity, and the detected human power detection value is electrically entered into the control means. Therefore, when human power torque is not entered, the movable detection part of the torque sensor is in the initial position. And, when the human power torque is entered, the movable detection part of the torque sensor moved from its initial position to follow in proportion to the entered human power torque up to the maximum position.
Therefore, the mechanism which performs the zero point adjustment of the torque sensor by the electrical adjusting element has a torque sensor which outputs the detected human power torque signal as a voltage value, adds an offset voltage to the output voltage to perform zero point adjustment, and dispose on a circuit board a control knob for adjusting the offset voltage.
A mechanism for mechanically adjusting zero point is often configured with an adjusting screw disposed in the neighborhood of the movable detection part of the torque sensor, this adjusting screw is used to adjust in order to decide the initial position which is the mechanical zero point of the torque sensor.
For example, Japanese Patent Laid-Open Publication No. Hei 5-246377 and Japanese Patent Laid-Open Publication No. Hei 5-310177 indicate a torque sensor 565 having the structure as shown in FIG. 55 as an example of the torque sensor structure.
This torque sensor 565 is structured that when the user applies leg power to the pedals of a bicycle as the human power drive force, a leg power detection lever 564 is accordingly rotated in a counterclockwise direction which is a forward direction. And, this leg power detection lever 564 has two projections 564a, 564b formed at a predetermined interval in the circumferential direction, the projection 564b is always in contact with a second lever 568, the projection 564a comes in contact with a stopper 566 when the leg power detection lever 564 comes in a predetermined angle position.
Therefore, when the leg power detection lever 564 rotates in the counterclockwise direction according to the human power torque, the projection 564b rotates the second lever 568 in the clockwise direction. And, since a potentiometer 572 which is a rotation angle sensor is connected with the rotating shaft of the second lever 568, a rotation angle of the lever 568 is measured by the potentiometer 572 to detect the human power torque as a current or voltage value and to output from the torque sensor 565.
On the other hand, when leg power is not entered, the second lever 568 is rotated counterclockwise by a return spring 570 which is in contact with the second lever 568 the leg power detection lever 564 is rotated clockwise in an opposite direction. And, when the leg power detection lever 564 comes to a certain rotation angle position, the projection 564a of the leg power detection lever 564 comes in contact with the leading end of the stopper 566, so that the leg power detection lever 564 is prevented from moving further in the clockwise direction and stopped in the rotation position where it is.
Thus, the rotation angle position where the projection 564a of the leg power detection lever 564 comes in contact with the stopper 566 and stops is the zero point position of the torque sensor 565, and a rotation quantity detection value at the rotation angle position by the potentiometer 572 is a zero point correction value. And, although the above-mentioned patent applications do not describe, this zero point adjustment in actually used products is performed by adjusting the protruded level of the stopper 566 towards the leg power detection lever 564.
However, according to the torque sensor zero point adjusting mechanism described above, since the exclusive mechanical mechanism and the electrical adjusting element are required for the torque sensor zero point adjustment, the structure is made complex and the number of parts is increased, the part cost is increased, it is necessary to provide a step of setting the zero point of the adjusting mechanism in the assembling process, the assembling cost becomes high, and the production cost of the torque sensor as a whole increases.
Besides, in the conventional structure, when the adjustment is made once, the set zero point value is not reset, and if the torque sensor properties may change with time, zero point is deviated, and the human power detection value includes always a large error, causing an problem in human power assisting controlling. Furthermore, depending on the used conditions such as external temperature atmospheres for example, the torque sensor properties may be varied.
Therefore, in such a case, even if the user enters the same human power torque for each pedal input cycle, the human power torque value detected by the torque sensor changes to be higher or lower than its actual level, proper motor assistance is not effected, and a comfortable human power assisting feeling can not be obtained for the electric bicycle.
In addition, the torque sensor and the zero point adjusting mechanism are precision equipment for detecting torque with high accuracy and making adjustment, mounted deep in a motor and transmission mechanism, and accommodated into a casing for satisfactory protection, thereby preventing an erroneous detection due to external interference. When the user makes readjustment, it takes time and labors for disassembling and reassembling, and adjusting operation itself is required to be made delicately. Therefore, it is very hard for the user to make readjustment.
In view of above, the present invention aims to provide a zero point adjusting mechanism for a torque sensor which allows the sensor performance change with time and can be provided with improved reliability and safety without the necessity of using the mechanical structure and the electrical adjusting element for the zero point adjustment and the zero point adjusting operation in assembling for the drive force auxiliary device which is provided with the above-described sensor, to eliminate the zero point adjusting operation in assembling, and to make the zero point adjustment automatically at every use.